Vertical Variability in Leaf Traits and Environmental Conditions: Implications for Evapotranspiration and Net Ecosystem Exchange above the Amazon Rainforest

Land-surface representations in weather and climate models simplify the characterization of vegetation as a single layer with bulk environmental conditions. This approach overlooks the vertical variability in leaf traits and environmental conditions within the canopy. This research explores the vertical variability of plant ecophysiology and environmental measurements within the Amazon tropical rainforest during daytime, specifically at the ATTO site, during the late dry season. To characterize the canopy and its vertical variability, we categorized the canopy into three layers: the top layer (approximately the upper third of the canopy, 18-27 m), the medium layer (approximately the medium third of the canopy, 9-18 m), and the low layer (approximately the lower third of the canopy, 0-9 m) where leaf gas exchange measurements were conducted. Utilizing these layers, we developed a multi-layer model representation that calculates water and CO2 fluxes based on within canopy on-site observations. We conducted sensitivity analyses of the rainforest multi-layer representation to discern the significance of capturing vertical variability in leaf traits and environmental conditions for deriving net fluxes of water and CO2 of the forest. Current results show that measured leaf traits exhibit vertical variation within the canopy, indicating larger productivity in the top layer compared to the medium and low layers. Environmental conditions, such as incoming radiation in the top layer, fluctuate due to cloud presence. Temperature peaks in the top layer and reaches a minimum at mid-canopy. This results in a non-uniform mixing of the canopy air, maintaining a stable layer within the forest canopy that can potentially affect the distribution of scalars within the canopy. Ongoing analyses explore the similarities and differences between the CO2 exchange between the multi-layer representation and CO2 fluxes from eddy covariance systems, as well as the sensitivity of the former to vertical variability in leaf traits and environmental conditions. By doing so, we aim to gain knowledge on the relevance (or irrelevance) of characterizing vertical variability in land-surface representations and on important processes that may not be well captured yet by land-surface representations.